A space-time code (STC) is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas. STCs rely on transmitting multiple, redundant copies of a data stream to the receiver in the hope that at least some of them may survive the physical path between transmission and reception in a good enough state to allow reliable decoding. STCs have made their way into wireless standards for point-to-point communications.
Standard codes for simultaneous reception include, for example, the single-antenna hierarchical codes in Digital Video Broadcast-Terestrial (DVB-T) and MediaFLO (forward link only). For the simplest such code, the symbol constellation is chosen on the basis of two streams, a “high-priority” stream and “low-priority” stream. The intent is that the high-priority stream can be decoded by a large set of terminals at low signal-to-interference-plus-noise-ratio (SINR), while a “lucky” subset of these terminals with sufficiently high SINR can also decode the low-priority stream.
The key to success of the DVB-T codes is their simplicity. The high-priority stream can be decoded max-log-optimally with only a small complexity penalty imposed by the presence of the low-priority stream. These codes are designed generally for single-transmit-antenna systems.
It is desirable to have a method of space-time coding multiple data streams for transmission from multiple antennas that allows higher-priority data streams to be decoded optimally without a large complexity penalty brought by the presence of the low-priority stream.